Predicting insecticide resistance: mutagenesis, selection and response. (1/238)

Strategies to manage resistance to a particular insecticide have usually been devised after resistance has evolved. If it were possible to predict likely resistance mechanisms to novel insecticides before they evolved in the field, it might be feasible to have programmes that manage susceptibility. With this approach in mind, single-gene variants of the Australian sheep blowfly, Lucilia cuprina, resistant to dieldrin, diazinon and malathion, were selected in the laboratory after mutagenesis of susceptible strains. The genetic and molecular bases of resistance in these variants were identical to those that had previously evolved in natural populations. Given this predictive capacity for known resistances, the approach was extended to anticipate possible mechanisms of resistance to cyromazine, an insecticide to which L. cuprina populations remain susceptible after almost 20 years of exposure. Analysis of the laboratory-generated resistant variants provides an explanation for this observation. The variants show low levels of resistance and a selective advantage over susceptibles for only a limited concentration range. These results are discussed in the context of the choice of insecticides for control purposes and of delivery strategies to minimize the evolution of resistance.  (+info)

Rainbow trout leucocyte activity: influence on the ectoparasitic monogenean Gyrodactylus derjavini. (2/238)

The ectoparasitic monogenean Gyrodactylus derjavini from rainbow trout Oncorhynchus mykiss was exposed in vitro to macrophages isolated as peritoneal exudate cells or as pronephros cells from the host. Cells colonized the parasite especially in the mannose-rich regions in the cephalic ducts where ciliated structures were abundant. Opsonization with fresh serum, in contrast to heat-inactivated serum, enhanced colonization also on other body parts. The adverse effect of the activated macrophages towards G. derjavini was associated with a heat-labile component released from these cells to the culture medium. Analysis of substances released from the cells showed reactivity for a number of enzymes, complement factor C3, interleukin (Il-1) and reactive oxygen metabolites. Chemotaxis assays with pronephric leucocytes showed chemoattractants in G. derjavini, and the respiratory burst level of macrophages was slightly elevated due to parasite exposure. It is suggested that skin leucocytes contribute to an increased level of complement factors in the trout skin during the host response, whereby a hostile microenvironment for the parasites is created. In addition, the IL-1 production could affect mucous cell secretion and hyperplasia and add to the antiparasitic action of the epithelium. Likewise, reactive oxygen metabolites and various enzymes are likely to be involved in the skin response.  (+info)

Changes in physiological parameters and feeding behaviour of Atlantic salmon Salmo salar infected with sea lice Lepeophtheirus salmonis. (3/238)

Atlantic salmon Salmo salar L. artificially infected with salmon lice Lepeophtheirus salmonis (Kroyer 1837) recovered from detrimental physiological changes and skin damage induced by preadult lice as the parasites matured. Growth rates of Atlantic salmon remained unaffected by lice infection, but food consumption decreased with increasing feeding and movement of the lice prior to and post-mating, correlating with the appearance of head erosions and detrimental changes in physiological integrity. Food consumption of the fish increased as the lice moulted to the adult stage and gravid female lice settled in a posterior location on the fish, subsequently reducing the impact of infection and allowing recovery of the skin damage. However, the impact of preadults was limited, as the decrease in food consumption of fish at 21 d post-infection had no effect on either the specific growth rate or condition factor of the fish. Furthermore, the intensity of lice infections at each of the sample days was not correlated with food consumption, specific growth rate or any of the haematological or physiological parameters measured, either before or after infection, indicating that lice intensity was independent of social dominance/subordinance. This work has provided the first evidence that infected fish can recover from the detrimental changes caused by lice infection, even when they are still infected with lice. If fish can survive the preadult stage of lice, then the mortal impact of lice infections is greatly reduced.  (+info)

Extent of gill pathology in the toadfish Tetractenos hamiltoni caused by Naobranchia variabilis (Copepoda: Naobranchiidae). (4/238)

Sanguinivorous Naobranchia variabilis prefer the first gill arch, external hemibranch and anterior end of the gill arch. The smallest N. variabilis observed attached to fish by a thin filament which connects fused tips of second maxillae to a 'plug' inserted into the gill tissue. Second maxillae enlarge to encircle and increasingly compress the gill filament, which results in a thin layer of epithelium and connective tissue overlying the cartilaginous supporting bar. Early juveniles cause little tissue proliferation, but the extent of proliferated epithelial and connective tissue (PR) adjacent to the maxillae increases from late juveniles to subadult and adult copepods. Most variation in length of gill filament damage (PL, proliferated and compressed tissue) among age classes is explained by maxilla length (ML, length of compressed gill filament); adult trunk width (TRW) explains an extra, small amount of variation, but not trunk length (TRL) or total fish length (TL). Most variation in ML is explained by TRW of adults, subadults and late juveniles, and TRL of early juveniles. PR is explained by TRW for adults, but by ML for other ages. These patterns are due to elongation of the juvenile trunk during growth and lateral expansion of adult egg pouches during maturation. Up to 38 N. variabilis, average (avg.) = 9.3, infected individual Tetractenos hamiltoni and damaged up to 3.4% (avg. 0.72%) of total filament length and 8.6% (avg. 2.1%) of gill filaments per fish.  (+info)

Chemical control of Haematobia irritans with 0.5% topical ivermectin solution in cattle. (5/238)

A field trial was conducted to evaluate the efficacy of a topical formulation of ivermectin administered at the dose of 500 micrograms/kg against horn flies (Haematobia irritans) in cattle. Eighty-eight cattle in four herds naturally exposed to horn flies were used in the trial. Replicates were formed of two herds. Within replicates, one herd was randomly allocated to the untreated control and the other to the ivermectin treatment group. Horn fly counts were taken on the treatment day (Day 0) and on Days 7, 14, 21, 28, and 35 post-treatment. There were no horn flies on any cattle in the treatment group, whereas all the control cattle were continuously infested by horn flies on each examination day.  (+info)

Carotenoids, sexual signals and immune function in barn swallows from Chernobyl. (6/238)

Carotenoids have been hypothesized to facilitate immune function and act as free-radical scavengers, thereby minimizing the frequency of mutations. Populations of animals exposed to higher levels of free radicals are thus expected to demonstrate reduced sexual coloration if use of carotenoids for free-radical scavenging is traded against use for sexual signals. The intensity of carotenoid-based sexual coloration was compared among three populations of barn swallows Hirundo rustica differing in exposure to radioactive contamination. Lymphocyte and immunoglobulin concentrations were depressed, whereas the heterophil:lymphocyte ratio, an index of stress, was enhanced in Chernobyl swallows compared to controls. Spleen size was reduced in Chernobyl compared to that of two control populations. Sexual coloration varied significantly among populations, with the size of a secondary sexual character (the length of the outermost tail feathers) being positively related to coloration in the two control populations, but not in the Chernobyl population. Thus the positive covariation between coloration and sexual signalling disappeared in the population subject to intense radioactive contamination. These findings suggest that the reliable signalling function of secondary sexual characters breaks down under extreme environmental conditions, no longer providing reliable information about the health status of males.  (+info)

Treatment of Microcotyle sebastis (Monogenea: Polyopisthocotylea) infestation with praziquantel in an experimental cage simulating commercial rockfish Sebastes schlegeli culture conditions. (7/238)

The antiparasitic efficacy of praziquantel against the blood-sucking polyopisthocotylean Microcotyle sebastis was tested in an experimental cage simulating commercial rockfish-culture conditions. Juvenile rockfish Sebastes schlegeli were separated into 4 pilot net-pens, and the fish in the groups were either fed a control diet (Group C), fed a praziquantel-adsorbed diet (Group F), bathed in 100 ppm praziquantel for 4 min (Group B), or bathed in 100 ppm praziquantel for 4 min and then fed a praziquantel-adsorbed diet (Group BF). The results of the present study indicate that feeding a praziquantel-adsorbed diet significantly reduces the abundance of M. sebastis infestation, and bathing in 100 ppm praziquantel for 4 min is effective for controlling M. sebastis infestation in practical rockfish culture systems.  (+info)

Bovine teat atresia associated with horn fly (Haematobia irritans irritans (L.))-induced dermatitis. (8/238)

Mammary gland lesions characterized primarily as mammary teat atresia were observed in a Limousin beef cattle herd in eastern Texas. Atresia of multiple teats per mammary gland was reported in first-calf heifers at the time of calving. Pathogens were not identified in eight mammary glands collected at slaughter. Histology of affected glands demonstrated superficial and deep perivascular inflammation and fibrosing dermatitis of teat and mammary gland skin that resulted in formation of the atretic lesions of glandular tissue. Institution of a horn fly (Haematobia irritans irritans (L.)) control program using insecticide-impregnated ear tags was associated with elimination of the problem from the herd.  (+info)